SPL PASSEQ Passive Mastering Equalizer for Pro Audio Applications (All Black) - Manual (Page 16)

12
Control Elements
Layout of Control Elements
Initially one might be struck by the circular arrangement of the PASSEQ’s control ele-
ments. As unusual as this first appears, the more understandable and clearer this layout
becomes when one looks closer.
Along with the fact that we simply like this design from an aesthetical view, this layout
makes even more sense with respect to the idea of the passive EQ concept itself: In a pas-
sive design, filters for boosting and cutting a frequency range are physically separated
from each other. Reflecting this fact, the elements left of the central output control per-
form level cuts, while controls to the right of this central regulator serve as signal boost
controls. Cut and boost switches are positioned next to the appropriate frequency band
selector and frequency bands are arranged from low to high from the standpoint of both
physical and frequency range layout.
Frequency
Each channel provides three cut and three boost frequency switches. You can choose 12
different frequencies per switch. The workable frequency range stretches from 10 Hz to
35 kHz.
Frequency Range:
• LF- (Low Frequencies Cut): 30 Hz bis 600 Hz
• LF+ (Low Frequencies Boost): 10 Hz bis 550 Hz
• MF- (Mid Frequencies Cut): 200 Hz bis 6 kHz
• MF+ (Mid Frequencies Boost): 220 Hz bis 4,8 kHz
• HF- (High Frequencies): 580 Hz bis 22 kHz
• HF+ (High Frequencies): 5 kHz bis 35 kHz
LF+ and LF-
The LF- frequency range extends from 30 Hz to 600 Hz. The low boost LF+ band encom-
passes a range of 10 Hz to 550 Hz. The maximum available increase in this LF+ boost band
is 17 dB, while the maximum reduction of the LF- band is 22 dB. Optically these filter
bands may be represented as having a shelving characteristic with an 6 dB slope. Passive
filters do not allow for direct alteration of the slope gradient because this quality is pre-de-
termined by component selection and not, as with active filters, by a variable value. The
lowest frequencies begin here with 10 Hz, then follow with 15 Hz, 18Hz, 26Hz, 40 Hz, and
so on. At this point one might think that such a lavish set of frequency choice in this range
might be a bit overdone, as there is acoustically a rather limited amount of audio mate-
rial of any real significance below 26 Hz. However, these choices are anything but arbi-
trary. These frequencies represent a consistent -3 dB point of a sloping down response
curve. That is, the gentle 6 dB slope also allows frequencies above 10 Hz to be processed.
As mentioned in other parts of this text, special condenser/coil/resistor filter networks
have been designed for each frequency range. The choice of one or the other inductances
produces differences in sonic coloration even when limited differences between frequen-
cies such as 10 Hz or 15 Hz play a subordinate role. Along with this differing phase rela-
tionships may come into play and affect tonal color. Because modern productions often
demand a definite number of choices in an engineer’s options for achieving an optimal
result in bass emphasis, the PASSEQ has been designed with a very complete set of low
frequency options to insure realizing these goals.